1. Field of the Invention
The invention relates to a display device (referred below to an FED (Field Emission Display)), which makes use of electron source elements (electron emitting elements). Also, the invention relates to a method of driving the FED. Further, the invention relates to an electronic equipment making use of the FED.
2. Description of the Related Art
An explanation will be given to an FED (Field Emission Display) making use of an electron source element. Here, an element emitting electrons owning to the electric field effect is referred to as an electron source element.
Electron source elements arranged on respective pixels of the FED emit electrons from electrodes due to the electric field effect. Electrons thus emitted are accelerated to be incident upon a fluorescent body. The fluorescent body in a region, upon which electrons are incident, emits light. A quantity of electrons emitted from the electron source elements on the respective pixels is controlled by a video signal input into the FED. The more electrons emitted, the higher emission luminance of the fluorescent body in the case where these electrons are incident upon the fluorescent body. Thus the FED represents gradation.
Electron source elements have various configurations. There are typically given an FE (Field Emission) type element for causing electrons to be emitted from a tip end of a convex electrode where an intense electric field is locally generated, a surface conduction type element for causing generation of electrons through flowing of an electric current in parallel to a thin film surface broken locally, an MIM (Metal-Insulator-Metal) type element composed of a first electrode, a second electrode and an insulating film interposed between the first electrode and the second electrode, and for emitting electrons upon application of voltage between the first electrode and the second electrode.
Here, what is regarded as important in electron source elements used in FEDs is whether elements can be made minute, or whether elements having a uniform performance can be fabricated, or whether elements can be driven with low voltage. Hereupon, MIM type electron source elements meeting these qualifications have been developed.
FIG. 6 shows an example of an MIM type electron source element. Its structure is described in SID 01 Digest page 193-195 xe2x80x9cNovel Device Structure of MIM Cathode Array for Field Emission Displaysxe2x80x9d.
In FIG. 6, formed on a substrate 20 with an insulating surface are a lower electrode 21, an upper electrode 23, and an insulating film 22 interposed between the lower electrode 21 and the upper electrode 23. Also, the reference numeral 24 denotes a protective insulating layer, 25a a contact electrode, 25b an upper electrode bus line, and 26 a protective electrode. In addition, a region where the upper electrode 23 overlaps an opening of the protective insulating layer 24 is referred to as an electron emission region and denoted by the reference numeral 27 in the figure.
Application of voltage between the upper electrode 23 and the lower electrode 21 causes injection of a hot carrier into the insulating film 22. That hot carrier of the hot carrier thus injected, which has a greater energy than a work function of a material of the upper electrode 23, passes through the upper electrode 23 to be emitted into the vacuum.
An MIM type electron source element having the structure shown in FIG. 6 emits electrons when voltage of around 10 V is applied between the upper electrode 23 and the lower electrode 21. In electron source elements, voltage applied between an upper electrode and a lower electrode when electrons are emitted is referred to as a drive voltage of an electron source element. An upper electrode of electron source elements is set to be high in electric potential as compared with a lower electrode thereof. In this manner, electrons are emitted from the upper electrode.
FIG. 7 shows an example of a display (FED) making use of the electron source element shown in FIG. 6. In addition, the same parts as those in FIG. 6 are denoted by the same reference numerals.
The FED shown in FIG. 7 has on the first substrate 20 with an insulating surface x (natural number) signal lines S1 to Sx arranged in a row direction, and y (natural number) scanning lines G1 to Gy arranged in a column direction. Electron source elements are arranged on respective points of intersection of the x signal lines S1 to Sx and the y scanning lines G1 to Gy. One electron source element, and that part of the signal lines and the scanning lines, to which the electron source element is connected, constitute one pixel. In FIG. 7, the reference numeral 300 denotes one pixel. The lower electrode 21 of the electron source element is connected to one of the y scanning lines G1 to Gy, and the upper electrode 23 is connected to one of the x signal lines S1 to Sx.
In addition, the lower electrode 21 may be connected to one of the x signal lines S1 to Sx and the upper electrode 23 may be connected to one of the y scanning lines G1 to Gy.
A second substrate 19 is provided to face that surface of the first substrate 20, on which the electron source element is provided. The second substrate 19 is light-transmissive. Arranged on the second substrate 19 is a fluorescent body 18 opposite to the electron source element. A black matrix 15 is arranged around the fluorescent body 18. In addition, the fluorescent body 18 is formed on a surface thereof with a metal-backed layer 17. Vacuum is kept between the first substrate and the second substrate.
A signal input into the scanning lines and a signal input into the signal lines cause emission of electrons from the upper electrode 23 in the electron source element of the pixel, in which voltage is applied between the upper electrode 23 and the lower electrode 21. Electrons thus emitted are accelerated in the vacuum 16 by voltage applied between the metal-backed layer 17 and the upper electrode. Electrons thus accelerated are incident upon the fluorescent body 18 provided on the second substrate 19 through the metal-backed layer 17. Thus the fluorescent body 18 in a region where electrons are incident emits light.
Here, a signal input into, for example, the scanning lines are kept constant in amplitude, and a signal input into the signal lines is varied in amplitude. A quantity of electrons emitted from the electron source element 28 is increased in accordance with voltage applied between the upper electrode 23 and the lower electrode 21. The more electrons emitted, the higher emission luminance can be represented in the case where these electrons are accelerated to be incident upon the fluorescent body 18 on the second substrate 19.
FIG. 8 shows a timing chart in the case where the display having the structure shown in FIG. 7 is driven. In the timing chart, one frame period (F) is a period, in which one picture image is displayed.
First, a scanning line G1 is selected. Here, other scanning lines G2 to Gy are put in a state, in which they are not selected. In addition, selection of a scanning line in FIGS. 7 and 8 means putting a scanning line connected to one of electrodes of an electron source element in a certain electric potential so that a quantity of electrons emitted from the electron source element is varied in accordance with an electric potential input into a signal line connected to the other of the electrodes of the electron source element.
For example, suppose that an electric potential of xe2x88x928 V is input into a scanning line as selected in the case where a scanning line is connected to the lower electrode 21 of the electron source element and a signal line is connected to the upper electrode 23. On the other hand, suppose that an electric potential of 8 V is input into scanning lines as not selected. Also, suppose that an electric potential of xe2x88x928 to 8 V is input into a signal line. Here, suppose that the upper electrode 23 of the electron source element emits electrons when the upper electrode 23 of the electron source element is higher about 10 V in electric potential than the lower electrode 21. At this time, the electron source element emits electrons when a signal electric potential of 5V from the signal line is input into the upper electrode 23 of the electron source element, of which the lower electrode 21 is connected to a scanning line in a selected state. Meanwhile, even when a signal electric potential of 5 V is input into the upper electrode 23 of the electron source element, of which the lower electrode 21 is connected to a scanning line in a non-selected state, the upper electrode 23 of the electron source element is lower in electric potential than the lower electrode 21 and so electrons are not emitted.
A period, in which the scanning line G1 is selected, is referred to as a first line period (L1). At this time, signals are successively input into the signal lines S1 to Sx. The electron source element emits electrons from the upper electrode 23 in accordance with signals as input. Thus emitted electrons cause the fluorescent body 18 provided on the opposed substrate 19 (second substrate) to emit light. In this manner, pixels in the first column emit light in accordance with signals as input. Subsequently, a scanning line G2 is selected. Here, G1, G3 to Gy are in a non-selected state. A period, in which the scanning line G2 is selected, is referred to as a second line period (L2). At this time, signals are successively input into the signal lines S1 to Sx. The electron source element 28 emits electrons from the upper electrode 23 in accordance with signals as input. Thus emitted electrons cause the fluorescent body 18 provided on the opposed substrate 19 (second substrate) to emit light. In this manner, pixels in the second column emit light in accordance with signals as input. The same action is repeated for all the gate signal lines, and so the one frame period is terminated. Thus the FED represents a picture image.
Since the above drive method is a passive type one, however, signals are directly input into electrodes of electron source elements of those pixels, on which display device should not be made. Therefore, there is involved a problem that power consumption is increased.
Hereupon, Japanese Patent Laid-Open No. 84927/2001 proposes an FED, in which a thin-film transistor (referred below to as a TFT) is arranged on each pixel. The constitution of this FED is shown in FIG. 9. FIG. 9 schematically shows electron source elements 902. The reference numeral 903 denotes lower electrodes, and 904 upper electrodes.
In FIG. 9, one of a source region and a drain region of a TFT 901 (referred below to as a pixel TFT) arranged every pixel is connected to one of x (natural number) signal lines S1 to Sx, and the other of the regions the lower electrode 903 of the electron source element 902. Also, a gate electrode of the pixel TFT 901 is connected to one of y (natural number) scanning lines G1 to Gy. The upper electrode 904 of the electron source element 902 is kept at a certain electric potential Vcom.
A selection signal is input into the scanning lines G1 to Gy. A pixel TFT 901 connected to a scanning line, into which a selection signal is input, is made ON. A signal input into a signal line is input into the lower electrode 903 of the electron source element 902 through the pixel TFT 901 having been made ON.
The electron source element 902 emits electrons due to a difference between an electric potential of the signal input into the lower electrode 903 and an electric potential of the upper electrode 904. Thus emitted electrons cause the fluorescent body to emit light, and so the pixel emits light. In addition, when the electron source element 902 emits electrons from the upper electrode 904, the upper electrode 904 is kept higher in electric potential than the lower electrode 903.
Power (reactive power) consumed in those pixels, in which display device should not be made (signals are not input into both scanning lines and signal lines), can be significantly reduced in a display device constructed such that the pixel TFT 901 is arranged in each pixel and a signal from a signal line is input into the lower electrode 903 of the electron source element 902 only in a pixel, in which the pixel TFT 901 is made ON.
An MIM type electron source element emits electrons when voltage is applied between an upper electrode and a lower electrode. Therefore, with pixels of a display device constructed in the manner described in Japanese Patent Laid-Open No. 84927/2001, voltage is applied between the upper electrode 904 and the lower electrode 903 of the electron source element 902 in a pixel, in which a signal is input into a scanning line to make the pixel TFT 901 ON, only for a period of time, during which a signal is input into a signal line, whereby electrons are emitted. Electrons are input into a fluorescent body only for a period of time, during which electrons are emitted, to cause a pixel emitting light.
For example, in the case where signals are input one pixel by one pixel from signal lines (dot sequential drive), a period of time, during which one pixel emits light, becomes equal to or less than 1/L of one frame period where the number of pixels possessed by a display device is L. Also, in the case where signals are input into all pixels in one column at the same time, that is, signals are input into pixels in one column at the same time from source signal lines S1 to Sx (line sequential drive), a period of time, during which one pixel emits light, becomes equal to or less than 1/y of one frame period assuming that a display possesses pixels of y columns.
Here, in the case where a display device such as large-sized displays, highly fine displays, or the like has a large number of pixels, a period of time, during which one pixel continues to emit light, becomes short in a display, in which pixels are constructed in the above manner. Therefore, when it is tried to represent an adequate luminance during one frame period, it becomes necessary to apply a high voltage between an upper electrode and a lower electrode of an electron source element in a short period of time. Therefore, a drive circuit is increased in drive voltage and load on elements, which constitute the drive circuit, becomes large. Therefore, there is caused a problem that a display device is degraded in reliability.
Also, in order to input analog signals into signal lines S1 to Sx, a plurality of signal voltages must be set to meet respective graduations. Therefore, there is caused a problem that such construction is not suited to multi-graduations.
Hereupon, the invention has its object to realize action with low power consumption, high reliability and multi-graduations in an FED.
Arranged on respective pixels are an electron source element, a first TFT, a second TFT, and a capacitor element. The first TFT is referred to as a switching TFT, and the second TFT is referred to as a drive TFT.
A gate electrode of the switching TFT is connected to a scanning line, and one of a source region and a drain region of the switching TFT is connected to a signal line, the other being connected to a gate electrode of the drive TFT and one of electrodes of the capacitor element (storage capacitor). The other electrode of the capacitor element is connected to a power feed line. One of a source region and a drain region of the drive TFT is connected to a power feed line, and the other is connected to one of electrodes of the electron source element.
In addition, in the case of making positive use of a parasitic capacitance of a gate of the drive TFT, the above capacitor element is not necessary needed.
With the pixel constructed in the above manner, a signal electric potential is input into the gate electrode of the drive TFT through between source drains of the switching TFT. Here, the capacitor element (storage capacitor) preserves a gate voltage of the drive TFT having been varied by the signal electric potential as input.
The drive TFT having been made ON by the signal electric potential input into the gate electrode imparts a predetermined electric potential to one of electrodes of the electron source element through between source drains thereof. For example, electric potential substantially equivalent to electric potential of the power feed line. In this manner, voltage is applied between an upper electrode and a lower electrode of the electron source element, which in turn emits electrons. Here, voltage held by the storage capacitor continues to be preserved until a signal is input through the switching TFT from a signal line. In the meantime, the electron source element continues to emit electrons, and the pixel associated therewith continues to emit light.
With the above constitution, a signal once input into a pixel is preserved and so the pixel continues to emit light. Therefore, it becomes possible to set a light emitting period per one frame period to be long. In this manner, it is possible to decrease luminance per unit time. That is, voltage applied between both electrodes (upper electrode and lower electrode) of the electron source element can be set to be low. Accordingly, a display can be realized, which acts with low power consumption. Also, in the event of using the above drive method, since signal output having a high amplitude voltage is not required for a drive circuit, load on elements constituting the drive circuit is small. Thus it is possible to realize a display with high reliability.
Also, the time gradation system may be used in a display device having a pixel of the above constitution. In the time gradation system, one frame period is divided into a plurality of sub-frame periods, and a ON or OFF state of a drive TFT of respective pixels is selected in respective sub-frame periods, so that a light emitting or non-emitting state of respective pixels is selected. In a particular pixel, luminance is represented by adding up periods, in which a light emitting state is selected in one frame period.
With the above drive method, the number of gradations can be optionally set in accordance with a way to divide sub-frame periods. Therefore, the method is suited to multi-graduations as compared with a display device, in which voltage is varied stepwise to represent gradations.
In this manner, it is possible to realize action with low power consumption, multi-graduations and high reliability in an FED.
Examples of the constitution of a display device according to the invention and of a method of the same will be enumerated.
A display device according to the invention having an electron source element, from which electrons are emitted by applying a voltage between a first electrode and a second electrode, has a feature in that it comprises a capacitor element, a first signal line, a first switch, by which connection of one of electrodes of the capacitor element and the first signal line is selected, a second switch, which is switched over between ON and OFF in accordance with a voltage preserved in the capacitor element, and a second signal line connected to the first electrode of the electron source element through the second switch.
A display device according to the invention having an electron source element, from which electrons are emitted by applying a voltage between a first electrode and a second electrode, has a feature in that it comprises a capacitor element, a first signal line, a switch, by which connection of one of electrodes of the capacitor element and the first signal line is selected, and an element for varying an electric potential of the first electrode of the electron source element in accordance with a voltage preserved in the capacitor element.
A display device according to the invention having an electron source element, from which electrons are emitted by applying a voltage between a first electrode and a second electrode, has a feature in that it comprises a capacitor element, a first signal line, a first switch, by which connection of one of electrodes of the capacitor element and the first signal line is selected, a second switch, which is switched over between ON and OFF in accordance with a voltage preserved in the capacitor element, and a third switch for short-circuiting two electrodes of the capacitor element.
The electron source element is composed of the first and second electrodes, and an insulating layer between the first and second electrodes.
A display device according to the invention having an electron source element, from which electrons are emitted by applying a voltage between a first electrode and a second electrode, has a feature in that it comprises a first signal line, a second signal line, a third signal line, a first TFT, and a second TFT, and that a gate electrode of the first TFT is connected to the second signal line, and that one of a source region and a drain region of the first TFT is connected to a gate electrode of the second TFT, the other being connected to the first signal line, and one of a source region and a drain region of the second TFT is connected to the third signal line, the other being connected to the first electrode of the electron source element.
A display device according to the invention having an electron source element, which is composed of a first electrode, a second electrode, and an insulating layer between the first electrode and the second electrode, and in which the first electrode is higher in electric potential than the second electrode and the first electrode emits electrons, has a feature in that it comprises a first signal line, a second signal line, a third signal line, a first TFT, and a second TFT, and a gate electrode of the first TFT is connected to the second signal line, and that one of a source region and a drain region of the first TFT is connected to a gate electrode of the second TFT, the other being connected to the first signal line, and one of a source region and a drain region of the second TFT is connected to the third signal line, the other being connected to the second electrode of the electron source element.
A display device according to the invention having an electron source element, which is composed of a first electrode, a second electrode, and an insulating layer between the first electrode and the second electrode, and in which the first electrode is higher in electric potential than the second electrode and the first electrode emits electrons, has a feature in that it comprises a first signal line, a second signal line, a third signal line, a first TFT, and a second TFT, and a gate electrode of the first TFT is connected to the second signal line, and that one of a source region and a drain region of the first TFT is connected to a gate electrode of the second TFT, the other being connected to the first signal line, and one of a source region and a drain region of the second TFT is connected to the third signal line, the other being connected to the first electrode of the electron source element.
The display device has a feature in that it comprises a capacitor element provided between a third electrode and a fourth electrode to preserve voltage, and that the third electrode is connected to the third signal line, and the fourth electrode is connected to a gate electrode of the second TFT.
A display device according to the invention having an electron source element, in which voltage is applied between a first electrode and a second electrode to emit electrons, has a feature in that it comprises a first signal line, a second signal line, a third signal line, a fourth signal line, a first TFT, a second TFT, a third TFT, and a capacitor element provided between a third electrode and a fourth electrode to preserve voltage, and a gate electrode of the first TFT is connected to the second signal line, that one of a source region and a drain region of the first TFT is connected to a gate electrode of the second TFT, the other being connected to the first signal line, one of a source region and a drain region of the second TFT being connected to the third signal line, the other being connected to the first electrode of the electron source element, and a gate electrode of the third TFT is connected to the fourth signal line, and that one of a source region and a drain region of the third TFT is connected to the third electrode of the capacitor element, the other being connected to the third signal line, the fourth electrode of the capacitor element being connected to the third signal line.
A display device according to the invention having an electron source element, which is composed of a first electrode, a second electrode, and an insulating layer between the first electrode and the second electrode, and in which the first electrode is higher in electric potential than the second electrode and the first electrode emits electrons, has a feature in that it comprises a first signal line, a second signal line, a third signal line, a fourth signal line, a first TFT, a second TFT, a third TFT, and a capacitor element provided between a third electrode and a fourth electrode to preserve voltage, and a gate electrode of the first TFT is connected to the second signal line, that one of a source region and a drain region of the first TFT is connected to a gate electrode of the second TFT, the other being connected to the first signal line, one of a source region and a drain region of the second TFT being connected to the third signal line, the other being connected to the second electrode of the electron source element, and a gate electrode of the third TFT is connected to the fourth signal line, and that one of a source region and a drain region of the third TFT is connected to the third electrode of the capacitor element, the other being connected to the third signal line, the fourth electrode of the capacitor element being connected to the third signal line.
A display device according to the invention having an electron source element, which is composed of a first electrode, a second electrode, and an insulating layer between the first electrode and the second electrode, and in which the first electrode is higher in electric potential than the second electrode and the first electrode emits electrons, has a feature in that it comprises a first signal line, a second signal line, a third signal line, a fourth signal line, a first TFT, a second TFT, a third TFT, and a capacitor element provided between a third electrode and a fourth electrode to preserve voltage, and a gate electrode of the first TFT is connected to the second signal line, that one of a source region and a drain region of the first TFT is connected to a gate electrode of the second TFT, the other being connected to the first signal line, one of a source region and a drain region of the second TFT being connected to the third signal line, the other being connected to the first electrode of the electron source element, and a gate electrode of the third TFT is connected to the fourth signal line, and that one of a source region and a drain region of the third TFT is connected to the third electrode of the capacitor element, the other being connected to the third signal line, the fourth electrode of the capacitor element being connected to the third signal line.
An electronic equipment may use the display device.
A method, according to the invention, of driving a display device having an electron source element, from which electrons are emitted by applying a voltage between two electrodes, comprises selectively inputting an electric potential of a signal, which is input into a signal line, into one of electrodes of a capacitor element, to cause the capacitor element to preserve a predetermined voltage. Connection between a power line and one of the electrodes of the electron source element is selected in accordance with a voltage thus preserved. A potential difference is given between an electric potential of the one of the electrodes of the electron source element connected to the power line and an electric potential of the other of the electrodes. Thereby the electron source element emits electrons, and the electric potential thus emitted is incident upon a fluorescent body. Thus the fluorescent body emits light, and pixels are put in a light emitting state.
A method, according to the invention, of driving a display device having an electron source element, from which electrons are emitted by applying a voltage between two electrodes, comprises selectively inputting an electric potential of a signal, which is input into a signal line, into one of electrodes of a capacitor element, to cause the capacitor element to preserve a predetermined voltage. Connection between a power line and one of the electrodes of the electron source element is selected in accordance with a voltage thus preserved. In this manner, a potential difference is given between one of the electrodes of the electron source element connected to the power line and the other of the electrodes. Thereby, the electron source element emits electrons, and the electric potential thus emitted is incident upon a fluorescent body. Thus the fluorescent body emits light, and pixels are put in a light emitting state. A voltage preserved by the capacitor element is discharged to cut off connection between the power line and the one of the electrodes of the electron source element. Thus emission of electrons from the electron source element is stopped to put pixels in a light non-emitting state.
A method, according to the invention, of driving a display device having an electron source element, from which electrons are emitted by applying a voltage between a first electrode and a second electrode, the method comprises using a first signal to select an ON state of a first switch and inputting a second signal into a second switch. Thus an ON state of a second switch is selected. In addition, the state of the second switch is held. A third signal is input into the first electrode of the electron source element through the second switch in the ON state. A potential difference between an electric potential of the one of the electrodes of the electron source element, into which the third signal is input, and an electric potential of the other of the electrodes causes the electron source element to emit electrons, and the electric potential thus emitted is incident upon a fluorescent body. Thus the fluorescent body emits light, and pixels are put in a light emitting state.
A method, according to the invention, of driving a display device making use of an electron source element, from which electrons are emitted by applying a voltage between a first electrode and a second electrode, comprises inputting a first digital signal into a gate electrode of a first TFT to select an ON state of the first TFT. Thus a second digital signal is input through between source/drain of the first TFT in the ON state into a gate electrode of a second TFT. An ON state of the second TFT is selected by the second digital signal. An electric potential of a power source is input into the first electrode of the electron source element through between source/drain of the second TFT in the ON state to provide a predetermined voltage between the first electrode and the second electrode of the electron source element. Thus the electron source element emits electrons, and the electric potential thus emitted is incident upon a fluorescent body. Thus the fluorescent body emits light, and pixels are put in a light emitting state.
The second digital signal may be input into the second TFT several times during one frame period.
A method, according to the invention, of driving a display device having an electron source element, which is composed of a first electrode, a second electrode, and an insulating layer between the first electrode and the second electrode, and in which the first electrode is higher in electric potential than the second electrode and the first electrode emits electrons, comprises inputting a first digital signal into a gate electrode of a first TFT to select an ON state of the first TFT. A second digital signal is input through between source/drain of the first TFT in the ON state into a gate electrode of a second TFT. Thus an ON state of the second TFT is selected. An electric potential of a power source is input into the second electrode of the electron source element through between source/drain of the second TFT in the ON state to provide a predetermined voltage between the first electrode and the second electrode of the electron source element. Thus the electron source element emits electrons, and the electric potential thus emitted is incident upon a fluorescent body. Thus the fluorescent body emits light, and pixels are put in a light emitting state.
A method, according to the invention, of driving a display device having an electron source element, which is composed of a first electrode, a second electrode, and an insulating layer between the first electrode and the second electrode, and in which the first electrode is higher in electric potential than the second electrode and the first electrode emits electrons, comprises inputting a first digital signal into a gate electrode of a first TFT to select an ON state of the first TFT. A second digital signal is input through between source/drain of the first TFT in the ON state into a gate electrode of a second TFT. Thus an ON state of the second TFT is selected. An electric potential of a power source is input into the first electrode of the electron source element through between source/drain of the second TFT in the ON state to provide a predetermined voltage between the first electrode and the second electrode of the electron source element. Thus the electron source element emits electrons, and the electric potential thus emitted is incident upon a fluorescent body. Thus the fluorescent body emits light, and pixels are put in a light emitting state.
The second digital signal may be input into the second TFT several times during one frame period.
A gate voltage of the second TFT determined by the second digital signal may be preserved by a parasitic capacitance portion between the gate electrode and a source region or a drain region of the second TFT.
A method, according to the invention, of driving a display device making use of an electron source element, from which electrons are emitted by applying a voltage between a first electrode and a second electrode, comprises inputting a first digital signal into a gate electrode of a first TFT to select an ON state of the first TFT. A second digital signal is input through between source/drain of the first TFT in the ON state into a gate electrode of a second TFT to select an ON state of the second TFT. A capacitor element is used to preserve a gate voltage of the second TFT determined by the second digital signal. A predetermined electric potential of a power source is input into the first electrode of the electron source element through between source/drain of the second TFT in the ON state. A predetermined voltage is given between the first electrode and the second electrode of the electron source element. Thus the electron source element emits electrons, and the electric potential thus emitted is incident upon a fluorescent body. Thus the fluorescent body emits light, and pixels are put in a light emitting state. Also, a third TFT, which is connected in parallel to the capacitor element, is made ON to thereby discharge charge preserved by the capacitor element. Thus the second TFT is put in an OFF state, and the electron source element is caused not to emit electrons. Then pixels are put in a light non-emitting state.
An electronic equipment may use a method of driving the above display device.